The presence of a great white sharks hunting close to swimmers...a disturbing thought!

On Saturday, Paul Bremser was at Chatham's Lighthouse Beach preparing to go surfing. He had one leg into his wetsuit when he heard someone yell, ''Shark!''

He looked up to see a big fin circling a seal, just beyond the breakers about 75 feet away.

A great white shark swims in the Monterey Bay Aquarium in Monterey, Calif., in late September 2004. (Associated Press photo)

''After it came around in a full circle, the shark came off from the back side and cut him in half with one bite,'' said Bremser, a commercial fishermen with 28 years of experience fishing out of Chatham. The seal tried to swim away as a pool of blood spread around it. The shark went down, then the seal dropped out of sight.

''It's a classic, textbook, attack pattern for a great white,'' said Greg Skomal, shark expert for the state Division of Marine Fisheries.

The sight of a great white shark hunting down seals among swimmers and surfers is not comforting and could be the start of a disturbing trend.

In the 1970s, fewer than 20 gray seals frequented the waters of southern New England.

Since then, with marine mammal protection regulations in place, the seal population has exploded to about 6,000 on the Monomoy islands, making it home to one of the largest seal colonies in New England.

Lighthouse Beach is just a couple of miles from Monomoy.

''With an increasing seal population, in all likelihood we may see a redistribution of white sharks to target that,'' Skomal said.

Two years ago, Skomal tagged a 14-foot, 1,700-pound great white that was trapped in a shallow lagoon and coastal waters off Naushon Island for two weeks.

GREAT WHITE SHARKS

Great white sharks are the top predators of the sea. Their favorite prey is sea mammals, especially sea lions and seals. The only animals to attack great white sharks are other great whites and orcas.

Great whites can grow nearly 20 feet long and weigh up to 5,000 pounds. The average length is 10 to 15 feet.

Their skeletons are composed of cartilage. They are partially warm-blooded.

The sharks are highly migratory, moving over a vast area. They tend to be isolated from one another. Great white sharks live in almost all the cold or temperate waters of the planet, although they are rare off the New England coast.

Life span: Known to be 15 to 20 years, although scientists speculate they could live 30 to 40 years.
Appearance: Has a large conical-shaped snout, with same-size upper and lower lobes on its tail fin. Pale to dark gray, with a white belly.

But, he noted, great whites are still extremely rare in our waters. No great white has ever been hooked in the 19 years of the Martha's Vineyard shark fishing tournament, with more than 200 vessels participating each year. And Skomal has been trying in vain for two years to find another great white to tag, after the tag fell off the Naushon beast soon after it was freed.

In hundreds of years, Massachusetts has had only three possible attacks by great whites, the last one in 1938 in Buzzards Bay.

''You don't have very high attacks on people, even in South Africa (where there are far more sharks),'' Skomal said.

Yesterday, the news of the shark attack was all over Lighthouse Beach, but it didn't faze any of the beachgoers.

A half-dozen seals popped their heads up near swimmers yesterday.

Donna Wilcock stood knee-deep in the water on a sandbar as her 9-year-old daughter, Ashley, waded back to her through the small breakers. She had heard about the shark, but didn't tell her daughter.

''She would have felt sorry for the seal,'' she said. Wilcock summers in Chatham, but lives in Virginia and sometimes vacations in Florida where sharks and shark attacks are more common.
Saturday's seal attack occurred near a remote section of the beach about a half-mile away, and Wilcock didn't think twice about letting her daughter swim.

Chatham Town Administrator William Hinchey said the town had increased patrols on land and sea following the incident Saturday, but had seen no evidence of sharks in the area. He said the town would continue beefed-up patrolling into the near future.

Skomal ruled out seal eaters like the Greenland shark, which prefers deeper, colder waters far offshore, and the tiger shark, a tropical species found 60 miles or more out in the warmer waters of the Gulf Stream.

He said he would be coming to Chatham to look for the shark and tag it.